Before boat owners start taking their vessels out of dry dock, they ought to take their pens and pencils out of their pockets.

Then they ought to sit down and write their congressmen a pointed letter about a nasty little surprise in last year's agreement on the federal budget that didn't attract much attention until recently.Due to take effect this summer, the surprise involves a new tax on recreational boats. No tax is popular. This one is particularly odious because of the hypocrisy behind it.

The levy, which will range from $25 to $100 per vessel, applies to powerboats and sailboats over 16 feet long.

Though Congress tries to describe the tax as a user fee, it is no such thing. User fees are earmarked to provide services for the people who pay them. But the revenue raised by the new boat tax will go straight into the Treasury rather than to any specific agency providing services for boat owners and operators.

What's more, the new tax comes on top of a long list of levies already paid by boat owners - fuel excise taxes, registration fees, dockage fees, radio inspection fees and other charges.

There's hope for eliminating this burden, which amounts to a total of $127 million a year. This week a House subcommittee voted to repeal the new boat tax. But there's little prospect that the rest of Congress will go along unless the country's 4 million recreational boaters speak up loudly and tell the nation's lawmakers to sink the levy.